FIELD OF THE INVENTION
[0001] The present invention relates to methods for bleaching pulps and compositions suitable
for use in the bleaching of pulps. In particular, the compositions are suitable for
use as additives for adjustment of pH and/or control of the amount of unwanted substances
within a pulp during a pulp bleaching step. Also related to the present invention
is the use of said compositions, for example the use of said compositions in a pulp
preparation or a papermaking process, as well as bleaching methods for pulps using
said compositions.
BACKGROUND OF THE INVENTION
[0002] Traditional bleaching processes of pulps commonly employ alkaline hydrogen peroxide
as a bleaching agent. To that effect, hydrogen peroxide and a water soluble alkaline
compound, such as sodium hydroxide and/or water glass are introduced into the pulp
in order to improve whiteness and/or brightness of a wood pulp, a recycled paper pulp
or any other mechanical pulp, such as a pulp for papermaking processes. The use of
chelating agents like EDTA to remove some of the metal ions from the pulp prior to
adding peroxide allows the peroxide to be used more efficiently. Magnesium salts and
sodium silicate may also be added to improve bleaching with alkaline peroxide.
[0003] WO 94/12725 A1 discloses the use of metal hydroxide-aluminium chloride mixtures as an alkaline agent
in hydrogen peroxide bleaching of virgin wood pulps and recycled paper pulp.
WO89/03863 discloses the use of magnesium hydroxide with a particulate inorganic material (e.g.
kaolin clay) in paper making.
[0004] More recently (for example as disclosed in
Li et al., Pulp & Paper Canada 106:6 (2005), pages T125 to T129 "Using magnesium hydroxide (Mg(OH)
2) as the alkali source in peroxide bleaching at Irving paper") magnesium hydroxide
Mg(OH)
2 and magnesium oxide MgO have been employed to replace sodium hydroxide and water
glass, and to reduce the need for chelating agents and sodium silicate. Since magnesium
hydroxide and alkaline earth metal hydroxides in general have limited solubility in
water, only reduced amounts are discharged as waste water, making it economically
and environmentally attractive to use. However, magnesium hydroxide is not used in
a widespread manner due to issues with formation of deposits in the pulp resulting
from the reaction of Mg
2+ ions with soluble and colloidal wood components, in particular magnesium fatty acid
salts and resins. The presence of these deposits unfavourably affects paper machine
runnability and paper mill productivity. These problems have prevented alkaline earth
metal hydroxide assisted hydrogen peroxide bleaching to be employed more widely.
[0005] The problem of magnesium based fatty acid salts and resins in pulps has so far received
little attention in the specialised literature. It is therefore an aim of the present
invention to allow the widespread use of alkaline earth metal hydroxides or alkaline
earth metal oxides in the bleaching of pulps.
SUMMARY OF THE INVENTION
[0006] The present invention is defined in the appended claims.
[0007] In certain embodiments, the present invention is embodied by a method of bleaching
a pulp comprising the step of providing a composition for use in bleaching of pulps,
for example for use in bleaching of papermaking pulps, the composition comprising
one or more particulate alkaline earth metal oxides or alkaline earth metal hydroxides
or mixtures thereof and one or more pitch control additives. The pitch control additives
may be selected from talc, bentonite, zeolite, diatomaceous earth, cationic mica,
aluminium sulphate, polyaluminium chloride, and mixtures thereof.
[0008] According to one embodiment of the invention, the particulate alkaline earth metal
is selected from magnesium, calcium, or mixtures thereof. According to one embodiment
of the invention, the pitch control additive is micronized talc. According to one
embodiment of the invention, the pitch control additive is selected from bimodal talc
and cationic talc.
[0009] Certain embodiments of the composition according to the present invention may involve
an aqueous slurry. According to one aspect, the slurries may have a solids content
from 10 wt.-% to 75 wt.-% of the total slurry, such as from 25 wt.-% to 72 wt.-% of
the total slurry, or from 35 wt.-% to 70 wt.-% of the total slurry, or from 45 wt.-%
to 68 wt.-% of the total slurry, or from 50 wt.-% to 65 wt.-% of the total slurry,
such as about 55 wt.-% of the total slurry.
[0010] Certain embodiments of the composition according to the present invention may involve
pellets. According to one aspect, the pellets may have a moisture content from 0.1
wt.-% to 35 wt.-%, based on the total weight of the composition. According to a further
aspect, the pellets may comprise from 0.1 wt.-% to 50 wt.-% pitch control additive
and from 99.9 wt.-% to 50 wt.-% particulate alkaline earth metal oxide or alkaline
earth metal hydroxide or mixtures thereof, based on the total solids content of the
pellets.
[0011] Certain embodiments of the composition according to the present invention may involve
spray-dried particulate compositions. According to one aspect, the said spray-dried
composition may have a moisture content of 5 wt.-% or less, based on the total dry
weight of the composition.
[0012] According to the present invention, the particulate alkaline earth metal oxide or
alkaline earth metal hydroxide is present in an amount ranging from 10 wt.-% to 90
wt.-%, and the pitch control additive present in an amount ranging from 90 wt.-% to
10 wt.-%, each on the basis of the total solids content of the composition. In one
embodiment, the particulate alkaline earth metal oxide or alkaline earth metal hydroxide
is present in an amount ranging from 30 wt.-% to 70 wt.-%, and the pitch control additive
is present in an amount ranging from 70 wt.-% to 30 wt.-%, each on the basis of the
total solids content of the composition. In one embodiment, the particulate alkaline
earth metal oxide or alkaline earth metal hydroxide is present in an amount ranging
from 40 wt.-% to 60 wt.-%, and the pitch control additive is present in an amount
ranging from 60 wt.-% to 40 wt.-%, each on the basis of the total solids content of
the composition. In one embodiment, the particulate alkaline earth metal oxide or
alkaline earth metal hydroxide is present in an amount of 50 wt.-% on the basis of
the total solids content of the composition. In one embodiment, the pitch control
additive is present in an amount of 50 wt.-%, on the basis of the total solids content
of the composition.
[0013] According to one embodiment of the present invention, the weight ratio of the particulate
alkaline earth metal oxide or alkaline earth metal hydroxide compared to the said
pitch control additive ranges from 9:1 to 1:9. In one embodiment, the weight ratio
of the particulate alkaline earth metal oxide or alkaline earth metal hydroxide compared
to the said pitch control additive ranges from 7:3 to 3:7. In one embodiment, the
weight ratio of the particulate alkaline earth metal oxide or alkaline earth metal
hydroxide compared to the said pitch control additive ranges from 6:4 to 4:6. In one
embodiment, the weight ratio of the particulate alkaline earth metal oxide or alkaline
earth metal hydroxide compared to the said pitch control additive is 1:1.
[0014] According to one embodiment, the composition may further comprise one or more of
the following additives: dispersants; fillers; surfactants; bleaching agents; chelating
agents; and pH-buffering agents.
[0015] The use of the composition according to certain embodiments of the present invention
in a pulp preparation or a papermaking process is another aspect of the invention.
In particular, bleaching methods for a pulp may comprise the step of providing a composition
according to certain embodiments of the invention and adding it to the pulp in such
an amount that the particulate alkaline earth metal oxide or alkaline earth metal
hydroxide is present in the pulp in an amount ranging from 0.1 to 8 wt.-%, and that
the pitch control additive is present in the pulp in an amount ranging from 0.1 to
8 wt.-%, each on the basis of the total solids content of the pulp after addition.
According to one embodiment, the method further comprises the addition of one or more
selected from hydrogen peroxide, water glass and a complexing agent to the pulp. According
to certain embodiments of the invention, the composition may be added to the pulp
during a bleaching step, or during a grinding step, or at any time between the grinding
and the bleaching step.
[0016] It is understood that the following description and references to the figures concern
exemplary embodiments of the present invention and shall not be limiting the scope
of the claims.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention according to the appended claims provides methods for bleaching
pulps making use of compositions for use in bleaching of pulps, for example compositions
for use in bleaching of papermaking pulps.
[0018] It has been found that a combination of alkaline earth metal hydroxide or alkaline
earth metal oxide with one or more pitch control agents, when used as an alkaline
additive in hydrogen peroxide bleaching of pulps, effectively reduces or eliminates
the formation of harmful deposits in the pulp. According to certain embodiments of
the present invention, the formation of harmful deposits in the pulp is reduced by
10% or more, such as by 30% or more, such as by 50% or more, or by 70% or more, for
example by 90%. According to certain embodiments, the formation of harmful deposits
in the pulp is reduced by more than 90%. According to certain embodiments of the present
invention, the alkaline earth metal hydroxide or alkaline earth metal oxide on the
one hand and the pitch control agents on the other hand are present in the composition
as discrete particles. As used herein, the term "discrete particles" signifies that
the particles are not dissolved (i.e., in solution) and/or not chemically or physically
bound and may be separated from each other by purely mechanical methods.
[0019] The alkaline earth metal hydroxide or alkaline earth metal oxide may be selected
from magnesium hydroxide, calcium hydroxide, magnesium oxide and calcium oxide, or
mixtures thereof. If an alkaline earth metal oxide is used, this acts in the same
way as an alkalinity agent by formation of the corresponding alkaline earth metal
hydroxide in aqueous medium. These compounds have a low solubility in water and are
therefore released into the pulp only at the rate they are being consumed during the
bleaching process, therefore providing improved control of the pH of the pulp. During
the bleaching process, the pH of the pulp may be 7 or higher, or ranging from 9 to
11.
[0020] In certain embodiments, the alkaline earth metal hydroxide may be magnesium hydroxide.
In some embodiments, the magnesium hydroxide may be crystalline (e.g., brucite). In
other embodiments, the magnesium hydroxide may be an amorphous form.
[0021] The pitch control agent for use in the composition according to certain embodiments
of the present invention is preferably talc, a natural magnesium silicate with a platy
structure. A combination of discrete talc and alkaline earth metal hydroxide or alkaline
earth metal oxide particles for use in hydrogen peroxide bleaching has not been previously
contemplated.
[0022] In one embodiment, the talc for use in the present invention may be present in combination
with impurities, such as chlorite and/or carbonates. In one embodiment, the composition
for use in bleaching pulps may further comprise impurities such as chlorite and/or
carbonates.
[0023] In one embodiment, the talc for use in the present invention is micronised talc.
Micronised talc is ground talc having a median particle diameter d
50, as measured in a Sedigraph, ranging from 0.5 µm to 15 µm. Preferably the micronized
talc for use in the composition according to certain embodiments of the present invention
has a median particle size d
50, ranging from 1.5 µm to 6.5 µm, more preferably from 2 µm to 4 µm, or from 2.0 µm
to 4.0 µm.
[0024] Particle size characteristics described herein are measured via sedimentation of
the particulate material in a fully dispersed condition in an aqueous medium using
a Sedigraph 5100 particle size analyzer supplied by Micrometrics Instruments Corporation
Norcross, Ga, USA. The term "d
50" as used herein refers to the median particle diameter and is the particle diameter
at which 50% by weight of the product is larger and 50% by weight is smaller.
[0025] In one embodiment, the talc for use in the composition is bimodal talc. A bimodal
talc as used herein is a particulate talc, wherein an envelope curve of size distribution
of the particles obtained by sedimentation using a Sedigraph exhibits two distinct
peaks. As used herein, the "envelope curve of particle size distribution" denotes
the curve of size distribution of all the talc particles in a specific sample. For
example, the envelope curve of particle size distribution of the talc contained in
a composition according to certain embodiments of the present invention denotes the
curve of size distribution of all the talc particles in the said composition. In one
embodiment, the bimodal talc as used in the composition may have peaks in the envelope
curve of particle size distribution located at any two of 0.2 µm, 0.5 µm, 1µm, 2 µm,
3 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, 9 µm, 10 µm, 11 µm, 12 µm, 13 µm, 14 µm, and 15
µm, or thereinbetween. For example, the bimodal talc as used herein may have peaks
in the envelope curve of particle size distribution at 0.5 µm and 4 µm, or at 1 µm
and at 6 µm. As defined herein, according to measurement uncertainties known to the
skilled person, the peaks in the envelope curve of particle size distribution may
be in the range of up to 100% above or below the given particle size, or for example,
they may be in the range of 90% above or below the given particle size, or for example,
they may be in the range of 80% above or below the given particle size, or for example,
they may be in the range of 70% above or below the given particle size, or for example,
they may be in the range of 60% above or below the given particle size, or for example,
they may be in the range of 50% above or below the given particle size, or for example,
they may be in the range of 40% above or below the given particle size, or for example,
they may be in the range of 30% above or below the given particle size, or for example,
they may be in the range of 20% above or below the given particle size, or for example,
they may be in the range of 10% above or below the given particle size, or for example,
they may be in the range of 5% above or below the given particle size.
[0026] In one embodiment a bimodal talc may have a particle size distribution such that
the peaks in the envelope curve of particle size distribution have a relative size
of from 9:1 to 1:9, for example a relative size of from 8:2 to 2:8, for example a
relative size of from 7:3 to 3:7, for example a relative size of from 6:4 to 4:6,
such as for example a relative size of about 1:1. The relative size of the peaks is
defined as the ratio of the areas below the peaks.
[0027] In one embodiment according to the present invention, the talc for use in the composition
is cationic talc. Cationic talc as used herein is talc, the surface of which has been
pretreated with a cationic polymer (e.g. PolyDADMAC) to change the anionic zeta potential
of untreated talc to a cationic zeta potential. In one embodiment, the cationic zeta
potential of the talc for use in the composition according to the present invention
is 10 mV or above, such as for example 20 mV or above.
[0028] According to certain embodiments of the present invention, the composition for use
in bleaching of pulps may be present as an aqueous slurry. Aqueous slurries are commonly
used, for example in papermaking, for introducing solids into a pulp. As such, a composition
according to certain embodiments of the present invention in the form of an aqueous
slurry may be introduced into the pulp in order to support hydrogen peroxide bleaching.
By putting certain embodiments of the composition of the present invention in the
form of a slurry, the overall weight of the composition is increased. In order to
limit the weight increase, for example to maintain efficiency in transportation of
the compositions, it is preferred that the aqueous slurries comprising the composition
according to certain embodiments of the present invention have a solids content of
10 wt.-% or higher, on the basis of the total weight of the slurry, such as 30 wt.-%
or higher, or 30 wt.-% or higher, or 40 wt.-% or higher, or 45 wt.-% or higher, or
50 wt.-% or higher, or even 60 wt.-% or higher, such as up to 70 wt.-%, or 72 wt.-%,
or 75 wt.-%. In order to achieve high solids content slurries, it may be necessary
to include dispersants in the slurry. The slurries may also comprise further components
such as fillers, surfactants, bleaching agents, pH-buffering agents, or other additives.
[0029] In certain embodiments, the composition has the form of dry particulate powders.
In order to reduce weight of the composition and to improve transportability, the
compositions may be transported as dry powders and slurries be formed only at the
site of use of the compositions in a bleaching process. The said dry particulate powders
may be obtained, for example, by use of a spray-drying process. Spray-dried particulate
compositions according to certain aspects of the present invention may have a low
or a very low moisture content, such as for example 5 wt.-% moisture or less, based
on the total amount of solids in the spray-dried particulate powder, or 4 wt.-% moisture
or less, or 3 wt.-% moisture or less, or even 2 wt.-% moisture or less, such as for
example about 1 wt.-% moisture or 0.5 wt.-% moisture. The dry compositions may also
comprise further components such as dispersants, fillers, surfactants, bleaching agents,
chelating agents, pH-buffering agents, or other additives.
[0030] In certain embodiments, the composition is in the form of pellets. According to one
aspect, the pellets may have a moisture content from 0.1 wt.-% to 25 wt.-%, based
on the total weight of the composition, such as for example from 2 wt.-% to 20 wt.-%
or from 5 wt.-% to 15 wt.-%, such as for example about 15 wt.-%. According to a further
aspect, the pellets may comprise from 2 wt.-% to 50 wt.-% pitch control additive and
from 98 wt.-% to 50 wt.-% particulate alkaline earth metal oxide or alkaline earth
metal hydroxide or mixtures thereof, based on the total solids content of the pellets.
[0031] For example, in one embodiment, the composition may be in the form of magnesium hydroxide/talc-pellets
comprising 87.5 wt.-% magnesium hydroxide and 12.5 wt.-% talc, each based on the total
solids content of the pellet.
[0032] According to certain embodiments of the present invention, the compositions for use
in bleaching of pulps may comprise the particulate alkaline earth metal oxides or
alkaline earth metal hydroxides and the pitch control additives in a weight ratio
ranging from 1:9 to 9:1, such as for example between 3:7 and 7:3, such as for example
ranging from 2:3 to 3:2, for example at a weight ratio of 1:2, or 1:1, or 2:1.
[0033] According to certain embodiments of the present invention, the compositions for use
in bleaching of pulps may comprise the one or more particulate alkaline earth metal
oxides or alkaline earth metal hydroxides in an amount of 10 wt.-% to 90 wt.-% of
the total solids content of the composition, such as for example in an amount of 30
wt.-% to 70 wt.-% of the total solids content of the composition, such as for example
in an amount of 40 wt.-% to 60 wt.-% of the total solids content of the composition,
such as for example in an amount of 50 wt.-% of the total solids content of the composition.
[0034] According to certain embodiments of the present invention, the compositions for use
in bleaching of pulps may comprise one or more pitch control additives in an amount
of 10 wt.-% to 90 wt.-% of the total solids content of the composition, such as for
example in an amount of 30 wt.-% to 70 wt.-% of the total solids content of the composition,
such as for example in an amount of 40 wt.-% to 60 wt.-% of the total solids content
of the composition, such as for example in an amount of 50 wt.-% of the total solids
content of the composition.
[0035] Also disclosed herein is the use of the compositions according to certain embodiments
of the present invention in the bleaching process of pulps, such as in the bleaching
process of pulps for papermaking. For example, the compositions according to certain
embodiments of the present invention may be used in combination with other additives
such as hydrogen peroxide, complexing agents, water glass, or others, in a bleaching
process of pulp in a paper making process.
[0036] The compositions for use in the method according to the present invention may fully
or partially replace known alkaline compositions, such as NaOH. For example, NaOH
may be fully omitted as the alkaline agent in a H
2O
2-bleaching process, or the amount of NaOH may be reduced by simultaneous addition
of a composition according to the present invention.
[0037] According to certain embodiments of the present invention, it is not required that
the one or more particulate alkaline earth metal oxides or alkaline earth metal hydroxides
or mixtures thereof on the one hand, and the one or more pitch control additives on
the other hand, be mixed together prior to being introduced into a pulp to be bleached.
An additional aspect of the present invention is the use of a composition obtained
by separately introducing the components of a composition into a papermaking pulp,
thereby forming the composition within a pulp during the bleaching of said pulp.
[0038] In the bleaching process, the composition according to certain embodiments of the
present invention is introduced into the pulp in such an amount that the amount of
the one or more particulate alkaline earth metal oxides or alkaline earth metal hydroxides
or mixtures thereof in the pulp is from 0.1 wt.-% to 8 wt.-% of the total solids content
of the pulp during the bleaching, such as from 0.2 wt.-% to 4 wt.-% of the total solids
content of the pulp during the bleaching, such as from 0.5 wt.-% to 2.5 wt.-% of the
total solids content of the pulp, such as for example 1 wt.-% or 2 wt.-% of the total
solids content of the pulp, and that the amount of the one or more pitch control additives
in the pulp is from 0.1 wt.-% to 8 wt.-% of the total solids content of the pulp during
the bleaching, such as from 0.2 wt.-% to 4 wt.-% of the total solids content of the
pulp during the bleaching, such as from 0.5 wt.-% to 2.5 wt.-% of the total solids
content of the pulp, such as for example about 1 wt.-% or about 2 wt.-% of the total
solids content of the pulp.
[0039] According to certain embodiments of the present invention, the composition for use
in bleaching of a papermaking pulp may be included in said pulp for example during
the bleaching stage, or at the beginning of the bleaching stage, or prior to the bleaching
stage. For example, the composition for use in bleaching of a papermaking pulp may
be included in said pulp as early as the grinding stage during which the pulp components
are ground, or at any time between the grinding stage and the bleaching stage. The
various components of the composition according to certain embodiments of the present
invention may also be added to the papermaking pulp at separate stages, such as for
example addition of the one or more pitch control agents during the grinding stage
and addition of the one or more particulate alkaline earth metal oxides or alkaline
earth metal hydroxides or mixtures thereof during or just prior initiation of the
bleaching step, or vice-versa.
EXAMPLES
[0040] The inventors have conducted a series of tests in order to demonstrate the efficiency
of the composition according to the present invention in pulp bleaching, and to investigate
the effect of the composition according to the present invention on deposit control.
[0041] In Examples 1, 2 and 3, hydrogen peroxide was used as 30% active content; NaOH was
used as a concentrated aqueous solution; Mg(OH)2 was used as a dry powder; DTPA was
used as a 50% active content solution; sodium silicate (water glass) was used in its
liquid aqueous form, of commercial quality. The talc employed had a mean particle
size d
50 of 3.5 µm as measured by Sedigraph. The heating was carried out in a water bath at
up to 90°C. The measurement of residual peroxide was carried out using standard iodometric
H
2O
2-titration, for example as known from
http://www.h2o2.com/technical-library/analytical-methods/default.aspx?pid=70&name=lodometric-Titration. Brightness, yellowness and Chemical oxygen demand (COD) were measured using standard
procedures: Brightness and yellowness were measured using ISO method 2470 in combination
with TAPPI method T 218 sp-02 for sheet preparation. The Chemical oxygen demand (COD)
was measured using a Hach-Lange Testkit and method LCK314 in combination with rapid
heating block HT 200S.
Example 1 - bleaching tests and waste water quality for medium bleaching level
[0042] Mechanical pulp samples (35 g dry weight) were bleached at 80°C for 150 minutes,
using 2.0% hydrogen peroxide and 0.30% DTPA in the presence of variable amounts of
NaOH, Mg(OH)2, talc, and water glass. The amounts of added water was always adjusted
to obtain a 30 % solids content in the pulp. The bleaching consistency was set to
30 %. The compositions used for bleaching to a medium level are listed in Table I:
Table I:
|
Comp. 1a |
Comp. 1b |
Comp. 1c |
Example 1 |
NaOH |
1.4% |
- |
0.7% |
- |
Mg(OH)2 |
- |
1.0% |
0.5% |
1.0% |
water glass |
1.5 % |
0.5% |
0.5% |
0.5% |
DTPA |
0.3% |
0.3% |
0.3% |
0.3% |
talc |
- |
- |
- |
1.0% |
[0043] Samples were taken from the bleaching mixtures after 75 and 150 minutes. The samples
were analysed for Brightness (% ISO) and Yellowness (%) to assess the bleaching efficiency,
and for residual peroxide (%) and COD (kg/t) to assess the waste water quality. The
results for an unbleached pulp sample ("Unbl.") are also shown. The results are shown
in Table II:
Table II:
|
Unbl. |
Comp. 1a |
Comp. 1b |
Comp. 1c |
Example 1 |
Sample (min) |
- |
75 |
150 |
75 |
150 |
75 |
150 |
75 |
150 |
Brightness (% ISO) |
72.0 |
80.00 |
79.43 |
79.08 |
80.04 |
79.83 |
80.00 |
78.75 |
79.63 |
Yellowness (%) |
16.5 |
12.38 |
12.89 |
12.95 |
12.77 |
12.70 |
12.80 |
12.75 |
12.51 |
Res. peroxide (%) |
0 |
35.14 |
33.40 |
54.33 |
44.03 |
40.41 |
36.57 |
52.00 |
40.19 |
COD (kg/t) |
11 |
46.68 |
34.63 |
35.35 |
34.61 |
[0044] The tests show that for medium bleaching levels, equivalent levels of colour and
brightness are achievable when NaOH is replaced by a composition according to the
present invention. The presence of talc as a pitching agent has no negative influence
on the bleaching performance. Furthermore, COD levels are 11 to 13 kg/t lower, showing
improved waste water quality, and residual peroxide is about 30 % higher, which allows
peroxide saving.
Example 2 - bleaching tests and waste water quality for medium bleaching level
[0045] Mechanical pulp samples (35 g dry weight) were bleached at 80°C for 150 minutes,
using 3.5% hydrogen peroxide and 0.30% DTPA in the presence of variable amounts of
NaOH, Mg(OH)2, talc, and water glass. The amounts of added water was always adjusted
to obtain a 30 % solids content in the pulp. The bleaching consistency was set to
30 %. The compositions used for bleaching to a medium level are listed in Table III:
Table III:
|
Comp. 2a |
Comp. 2b |
Comp. 2c |
Ex. 2a |
NaOH |
2.45% |
- |
1.25% |
1.25% |
Mg(OH)2 |
- |
1.7% |
0.85% |
0.85% |
water glass |
2.0% |
0.5% |
0.5% |
0.5% |
DTPA |
0.3% |
0.3% |
0.3% |
0.3% |
talc |
- |
- |
- |
1.0% |
[0046] Samples were taken from the bleaching mixtures after 75 and 150 minutes. The samples
were analysed for Brightness (% ISO) and Yellowness (%) to assess the bleaching efficiency,
and for residual peroxide (%) and COD (kg/t) to assess the waste water quality. The
results for an unbleached pulp sample ("Unbl.") are also shown. The results are shown
in Table IV:
Table IV:
|
Unbl. |
Comp. 2a |
Comp. 2b |
Comp. 2c |
Example 2a |
Sample (min) |
- |
75 |
150 |
75 |
150 |
75 |
150 |
75 |
150 |
Brightness (% ISO) |
72.0 |
82.06 |
82.41 |
80.79 |
81.25 |
81.55 |
82.28 |
81.29 |
81.65 |
Yellowness (%) |
16.5 |
10.89 |
10.86 |
11.77 |
11.67 |
11.27 |
10.96 |
11.03 |
10.97 |
Res. peroxide (%) |
0 |
31.06 |
26.84 |
44.87 |
36.68 |
39.63 |
35.60 |
38.20 |
30.83 |
COD (kg/t) |
11 |
60.90 |
40.93 |
50.70 |
47.75 |
[0047] The tests show that the compositions according to the present invention lead to an
approximately 1 % drop in brightness, if NaOH is fully substituted. However, a partial
(half) replacement of NaOH by a composition according to the present invention gives
equivalent bleaching results, better remaining peroxide and lower COD level. COD levels
are about 14 kg/t lower, showing improved waste water quality.
Example 3 - reduction of silicate (water glass) levels
[0048] Mechanical pulp samples (35 g dry weight) were bleached at 80°C for 150 minutes,
using 3.5% hydrogen peroxide and 0.30% DTPA in the presence of variable amounts of
NaOH, Mg(OH)2, talc, and water glass, in the same way as in Example 2. Reduction of
silicate (water glass) in the bleaching composition was tested. The compositions used
for bleaching to a medium level are listed in Table V:
Table V:
|
Comp. 2c |
Ex. 3a |
NaOH |
1.25 % |
1.25 % |
Mg(OH)2 |
0.85 % |
0.85 % |
water glass |
0.5 % |
0.25 % |
DTPA |
0.3 % |
0.3 % |
talc |
- |
1.0 % |
[0049] Samples were taken from the bleaching mixtures after 75 and 150 minutes. The samples
were analysed for Brightness (% ISO) and Yellowness (%) to assess the bleaching efficiency,
and for residual peroxide (%) and COD (kg/t) to assess the waste water quality. The
results for an unbleached pulp sample ("Unbl.") are also shown. The results are shown
in Table VI:
Table VI:
|
Unbl. |
Comp. 2c |
Example 3 |
Sample (min) |
- |
75 |
150 |
75 |
150 |
Brightness (% ISO) |
72.0 |
81.55 |
82.28 |
81.05 |
81.40 |
Yellowness (%) |
16.5 |
11.27 |
10.96 |
11.20 |
11.20 |
Res. peroxide (%) |
0 |
39.63 |
35.60 |
35.33 |
26.12 |
COD (kg/t) |
11 |
50.70 |
47.62 |
[0050] The tests show that reduction of silicate in the bleaching process slightly deteriorates
bleaching efficiency, but still leads to acceptable results, when a composition according
to the present invention is used. The use of lower silicate levels in the bleaching
process has a positive influence on anionic trash levels and improves machine runnability.
Example 4 - Deposit control
[0051] The effect of Mg(OH)
2 and talc on the tendency for resin deposit was tested. The test was carried out according
to the Gustafsson Method. Reactive additives (talc, NaOH, Mg(OH2)) are added to a
2 % aqueous fibre dispersion in an aluminium cup and mixed for 10 minutes using Gustafsson's
machine, an overhead stirrer with copper rotors. Then a resin, dissolved in acetone
is added, the resulting mixture is mixed for a further 30 minutes and the recipient
is rinsed with water. The resin deposits are extracted with acetone, the acetone is
evaporated and the weight of the resin deposit is measured.
[0052] The test was carried out in the presence of talc, NaOH and Mg(OH)
2 in various proportions. The results are shown in Table VII:
Table VII:
|
Comp. 4a |
Comp. 4b |
Comp. 4c |
Comp. 4d |
Ex. 4 |
Talc |
- |
2.0 % |
- |
- |
2.0 % |
NaOH |
- |
- |
0.2 % |
- |
- |
Mg(OH)2 |
- |
- |
- |
2.0 % |
2.0 % |
Deposit |
34 mg |
20 mg |
15 mg |
26 mg |
18 mg |
[0053] The test clearly shows that a mixture of Mg(OH)2 and talc leads to reduced resin
deposits, similar to those obtained when NaOH is used. This shows that the problem
known from the state of the art, of resin deposition in pulp during bleaching, can
be solved by adding a pitch control agent, such as talc, to an alkaline earth metal
oxides or hydroxide as the alkaline agent in H
2O
2-bleaching.
Example 5 - Granulation of Mg(OH)2
[0054] Various slurries comprising stabilised Mg(OH)
2 and talc were subjected to granulation in a standard pelletiser according to methods
known to the skilled person in the art. The slurries had a solids content of 54 wt.-%,
were dried in stainless steel containers and powdered and re-humidified using a Henschel
mixer.
[0055] The obtained pelletised compositions are shown in Table VIII:
Table VIII:
Ratio Mg(OH)2 (wt.-%) |
Ratio talc (wt.-%) |
Solid content prior to pelletisation |
Solid content after pelletisation |
Difference |
50 |
50 |
93.1 wt.-% |
94.6 wt.-% |
1.3 |
50 |
50 |
88.6 wt.-% |
89.3 wt.-% |
0.7 |
75 |
25 |
85.0 wt.-% |
86.7 wt.-% |
1.7 |
87.5 |
12.5 |
86.5 wt.-% |
86.7 wt.-% |
0.2 |
[0056] The listed solids contents are in respect to the total amount of material prior to
and after pelletisation. It was found that in the case of the 1:1 (weight) Mg(OH)2/talc
compositions, the formulation comprising more water lead to pellets with improved
adherence and stability. It was further found that, compared to pellets comprising
only 100wt.-% Mg(OH)2 (solids content), less energy was required to perform pelletisation.
1. Method of bleaching a pulp, comprising the step of providing a composition for use
in bleaching of pulps, the composition comprising
(a) one or more particulate alkaline earth metal oxides or alkaline earth metal hydroxides
or mixtures thereof; and
(b) one or more pitch control additives
wherein the content of the said particulate alkaline earth metal oxide or alkaline
earth metal hydroxide ranges from 10 wt.-% to 90 wt.-%, and the content of the said
pitch control additive ranges from 90 wt.-% to10 wt.-%, each on the basis of the total
solids content of the composition; and
the step of mixing said composition with the said pulp in such an amount that the
said particulate alkaline earth metal oxide or alkaline earth metal hydroxide is present
in the said pulp in an amount ranging from 0.1 to 8 wt.-%, and that said pitch control
additive is present in the said pulp in an amount ranging from 0.1 to 8 wt.-%, each
on the basis of the total solids content of the said pulp during bleaching.
2. Method according to claim 1, wherein said pitch control additive is selected from
talc, bentonite, zeolite, diatomaceous earth, cationic mica, aluminium sulphate, polyaluminium
chloride, and mixtures thereof.
3. Method according any of the previous claims, wherein the particulate alkaline earth
metal is selected from magnesium, calcium, and mixtures thereof.
4. Method according to any of the previous claims, wherein said pitch control additive
is selected from micronized talc, bimodal talc, and cationic talc.
5. Method according to any of the previous claims wherein the said composition is an
aqueous slurry.
6. Method according to claim 5, wherein said aqueous slurry has a total solids content
of from 10 to 75 wt.-%, on the basis of the total weight of the slurry.
7. Method according to any of the previous claims, wherein the weight ratio of the said
particulate alkaline earth metal oxide or alkaline earth metal hydroxide compared
to the said pitch control additive ranges from 9:1 to 1:9.
8. Method according to any of the previous claims, further comprising at least one of
the following additives: (a) dispersants; (b) fillers; (c) surfactants; (d) bleaching
agents; (e) chelating agents; and (f) pH-buffering agents.
9. Method according to any one of the previous claims, further comprising the addition
of one or more of hydrogen peroxide, water glass and a complexing agent to said pulp.
10. Method according to any one of the previous claims, wherein the said composition is
added to the said pulp during the bleaching step, or during the grinding step, or
between the grinding and the bleaching step.
11. Method according to any one of the previous claims, wherein the step of providing
a composition of any one of claims 1 to 10 comprises the sub-steps of
(a) providing one or more particulate alkaline earth metal oxides or alkaline earth
metal hydroxides or mixtures thereof;
(b) providing one or more pitch control additives; and
(c) adding the compositions obtained from sub-steps (a) and (b) separately to the
said pulp.
12. Method according to any one of the previous claims, wherein said method of bleaching
a pulp is a method of bleaching a pulp for papermaking.
1. Verfahren zum Bleichen einer Pulpe, umfassend den Schritt Bereitstellen einer Zusammensetzung
zur Verwendung im Bleichen von Pulpen, die Zusammensetzung umfassend
(a) ein oder mehrere teilchenförmige Erdalkalimetalloxyde oder Erdalkalimetallhydroxyde
oder Gemische davon; und
(b) ein oder mehrere Pechkontrollzusätze
worin der Gehalt des teilchenförmigen Erdalkalimetalloxyds oder Erdalkalimetallhydroxyds
im Bereich von 10 Gew.-% bis 90 Gew.-% ist, und der Gehalt des Pechkontrollzusatzes
im Bereich von 90 Gew.-% bis 10 Gew.-% ist, jeweils auf Grundlage des Gesamtfeststoffanteils
der Zusammensetzung; und
den Schritt Vermischen der Zusammensetzung mit der Pulpe in einer Menge, so dass das
teilchenförmige Erdalkalimetalloxyd oder Erdalkalimetallhydroxyd in der Pulpe in einer
Menge im Bereich von 0,1 bis 8 Gew.-% vorliegt, und dass der Pechkontrollzusatz in
der Pulpe in einer Menge im Bereich von 0,1 bis 8 Gew.-% vorliegt, jeweils auf Grundlage
des Gesamtfeststoffanteils der Pulpe während des Bleichens.
2. Verfahren gemäß Anspruch 1, wobei der Pechkontrollzusatz ausgewählt ist aus Talk,
Bentonit, Zeolith, Diatomeenerde, kationischem Glimmer, Aluminiumsulfat, Polyaluminiumchlorid
und Gemischen davon.
3. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, wobei das teilchenförmige
Erdalkalimetall ausgewählt ist aus Magnesium, Calcium und Gemischen davon.
4. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, wobei der Pechkontrollzusatz
ausgewählt ist aus mikronisiertem Talk, bimodalem Talk und kationischem Talk.
5. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, wobei die Zusammensetzung
eine wässrige Aufschlämmung ist.
6. Verfahren gemäß Anspruch 5, wobei die wässrige Aufschlämmung einen Gesamtfeststoffgehalt
von 10 bis 75 Gew.-% hat, auf Grundlage des Gesamtgewichts der Aufschlämmung.
7. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, wobei das Gewichtsverhältnis
des teilchenförmigen Erdalkalimetalloxyds oder Erdalkalimetallhydroxyds gegenüber
dem Pechkontrollzusatz im Bereich von 9:1 bis 1:9 ist.
8. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, zudem umfassend mindestens
einen der folgenden Zusätze: (a) Dispergiermittel; (b) Füller; (c) Oberflächenmittel;
(d) Bleichmittel; (e) Chelationsmittel; und (f) pH-Puffer.
9. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, zudem umfassend das Zusetzen
eines oder mehrerer aus Wasserstoffperoxyd, Wasserglas und einem Komplexierungsmittel
zur Pulpe.
10. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, wobei die Zusammensetzung
zur Pulpe während des Bleichungsschritts, oder während des Vermahlungsschritts, oder
zwischen dem Bleichungsschritt und dem Vermahlungsschritt zugesetzt wird.
11. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, wobei der Schritt Bereitstellen
einer Zusammensetzung in irgendeinem der Ansprüche 1 bis 10 die folgenden Unterschritte
umfasst
(a) Bereitstellen eines oder mehrerer teilchenförmiger Erdalkalimetalloxyde oder Erdalkalimetallhydroxyde
oder Gemische davon;
(b) Bereitstellen eines oder mehrerer Pechkontrollmittel; und
(c) separates Zusetzen der in Unterschritten (a) und (b) erhaltenen Zusammensetzungen
zur Pulpe.
12. Verfahren gemäß irgendeinem der vorhergehenden Ansprüche, wobei das Verfahren zum
Bleichen einer Pulpe ein Verfahren zum Bleichen einer Pulpe für die Papierherstellung
ist.
1. Procédé pour blanchir une pâte, comprenant l'étape de fournir une composition pour
l'utilisation dans le blanchiment de pâtes, la composition comprenant
(a) un ou plusieurs oxydes de métal alcalino-terreux ou hydroxydes de métal alcalino-terreux
particulaires ou leurs mélanges ; et
(b) un ou plusieurs additifs de contrôle de poix
où le contenu dudit oxyde de métal alcalino-terreux ou hydroxyde de métal alcalino-terreux
particulaire est dans l'intervalle de 10 pour cent en poids à 90 pour cent en poids,
et le contenu dudit additif de contrôle de poix est dans l'intervalle de 90 pour cent
en poids à 10 pour cent en poids, chacun à base du contenu en solides total de la
composition ; et
l'étape de mélanger ladite composition avec ladite pâte en une quantité telle que
ledit oxyde de métal alcalino-terreux ou hydroxyde de métal alcalino-terreux particulaire
est présent dans ladite pâte en une quantité dans l'intervalle de 0,1 à 8 pour cent
en poids, et que ledit additif de contrôle de poix est présent dans ladite pâte en
une quantité dans l'intervalle de 0,1 à 8 pour cent en poids, chacun à base du contenu
en soldes total de ladite pâte pendant le blanchiment.
2. Procédé selon la revendication 1, dans lequel ledit additif de contrôle de poix est
sélectionné parmi le talc, la bentonite, la zéolite, la terre de diatomées, le mica
cationique, le sulfate d'aluminium, le chlorure de polyaluminium, et leurs mélanges.
3. Procédé selon une quelconque des revendications précédentes, dans lequel ledit métal
alcalino-terreux particulaire est sélectionné parmi le magnésium, le calcium et leurs
mélanges.
4. Procédé selon une quelconque des revendications précédentes, dans lequel ledit additif
de contrôle de poix est sélectionné parmi le talc micronisé, le talc bimodal, et le
talc cationique.
5. Procédé selon une quelconque des revendications précédentes, dans lequel ladite composition
est une barbotine aqueuse.
6. Procédé selon la revendication 5, dans lequel la barbotine aqueuse a un contenu en
solides total de 10 à 75 pour cent en poids, à la base du poids total de la barbotine.
7. Procédé selon une quelconque des revendications précédentes, dans lequel le rapport
en poids dudit oxyde de métal alcalino-terreux ou hydroxyde de métal alcalino-terreux
particulaire par rapport audit additif de contrôle de poix est dans l'intervalle de
9:1 à 1:9.
8. Procédé selon une quelconque des revendications précédentes, comprenant en plus au
moins un parmi les additifs suivants : (a) dispersants ; (b) remplisseurs ; (c) agents
de surface ; (d) agents de blanchiment ; (e) agents chélateurs ; et (f) agents tampon
pH.
9. Procédé selon une quelconque des revendications précédentes, comprenant en plus l'addition
d'un ou de plusieurs parmi l'hydroxyde d'hydrogène, le silicate de métal alcalin et
un agent complexant à la pâte.
10. Procédé selon une quelconque des revendications précédentes, dans lequel ladite composition
est ajoutée à ladite pâte pendant l'étape de blanchiment, ou pendant l'étape de broyage,
ou entre l'étape de blanchiment et l'étape de broyage.
11. Procédé selon une quelconque des revendications précédentes, dans lequel l'étape de
fournir une composition d'une quelconque des revendications 1 à 10 comprend les sous-étapes
de
(a) fournir un ou plusieurs oxydes de métal alcalino-terreux ou hydroxydes de métal
alcalino-terreux particulaires ou leurs mélanges ;
(b) fournir un ou plusieurs additifs contrôle de poix, et
(c) ajouter les compositions obtenues des sous-étapes (a) et (b) séparément à ladite
pâte.
12. Procédé selon une quelconque des revendications précédentes, dans lequel ledit procédé
de blanchiment d'une pâte est un procédé de blanchiment d'une pâte pour la fabrication
de papier.